The present invention relates generally to electronic components, and, more particularly, to dispenser cathodes.
It is well known in the electronic field that electrodes are components of electric circuits that connect the conventional wiring of the circuits to conducting media. Examples of conducting media are metals, electrolytes or gasses.
In general, negatively charged electrodes are called cathodes, which are useful because they emit electrons. When a cathode becomes a source of electrons through a heating process, it is classified as a thermionic cathode. During cathode operation, free electrons are evaporated into the vacuum space at the cathode surface and repelled from the cathode surface because of its negative charge. These free electrons then become a useable electron flow.
Two primary types of thermionic cathodes are oxide cathodes and dispenser cathodes. Dispenser cathodes usually operate at temperatures between 900xc2x0 C. to 1200xc2x0 C. At these temperatures, thermal isolation of the cathode is necessary to minimize heat loss and to obtain stable electron emission. Such thermal isolation is achieved through use of refractory materials of minimum dimensions to limit thermal loss by conduction.
Impregnated dispenser cathodes are generally made from porous tungsten which is impregnated by barium compounds. When heated, the barium compounds react with the tungsten matrix. This reaction frees barium that subsequently migrates to the cathode emitter surface. Alternate variations of the porous matrix are made by mixing powders of tungsten and other refractory metals such as: iridium or osmium. Impregnated dispenser cathodes composed of these alternate variations are called mixed metal cathodes.
Impregnated cathodes characteristically have high emission current densities and long lives. They are preferred in thermoelectric tubes, such as: highly reliable microwave tubes used in satellite communication, linear accelerators, and high resolution image pickup or display tubes.
Impregnated dispenser cathodes designed for travelling wave tubes are generally supported by a complex design structure made from refractory materials. These designs require high temperature processing to affect refractory brazes and various other processes. Efficiency and life of the active element of a dispenser cathode can be compromised by these manufacturing thermal processes. More specifically, the active chemical compounds, necessary for cathode operation, can become compromised by inadvertent, but necessary, high temperature processing during the support structure construction. This inadvertent thermal processing causes chemical reactions to occur at very high rates, which subsequently reduces the efficiency and life of the cathode.
The disadvantages associated with conventional cathode construction have made it apparent that a new technique for cathode construction is needed. The new technique should substantially eliminate detrimental assembly processes. The new technique should also substantially minimize impurities on the emitter. The present invention is directed to these ends.
It is, therefore, an object of the invention to provide a construction method and design for a cathode system.
In one aspect of the invention, the cathode system includes an impregnated pellet and a first conductive cup which has first substantially cylindrical sides. The first conductive cup has a first open end sized to receive the impregnated pellet. The first conductive cup further has a first closed end. The first closed end has a first internal surface and a first external surface.
In another aspect of the invention, the cathode system includes a second conductive cup. The second conductive cup has second substantially cylindrical sides, which have a first diameter and a first length. The second conductive cup further has a second open end and a second closed end. The second closed end has a second internal surface and a second external surface, the second external surface of the second closed end of the second conductive cup electrically couples to the first external surface of the first closed end of the first conductive cup.
In still another aspect of the invention, the cathode system includes a third conductive cup. The third conductive cup also has third substantially cylindrical sides. The third substantially cylindrical sides have a second diameter less than the first diameter and a second length.
The first conductive cup receives the impregnated pellet following coupling of the first conductive cup to the second conductive cup and coupling of the second conductive cup to the third conductive cup.
The present invention thus achieves an improved cathode system and construction method. The present invention is advantageous in that it substantially eliminates residue on the emitter that usually results from the impregnating of the pellet. The present invention also facilitates cleaning of the cathode support structure without harm to the impregnated pellet.
Additional advantages and features of the present invention will become apparent from the description that follows and may be realized by the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.